1. Field of the Invention
The present invention relates to a polymer powder containing block polyetheramide based on an oligoamide dicarboxylic acid and on polyetheramines, preferably based on an oligoamide dicarboxylic acid and on polyetherdiamines, to the use of this powder in shaping processes, and also to moldings produced via a layer-by-layer process by which regions of a powder layer are selectively melted, using this powder.
2. Description of the Related Art
A task arising frequently in very recent times is rapid provision of prototypes. Particularly suitable processes are those whose operation is based on pulverulent materials and in which the desired structures are produced layer-by-layer via selective melting and hardening. Support structures for overhangs and undercuts can be omitted in these processes because the powder bed surrounding the molten regions provides sufficient support. The subsequent work of removing supports is also omitted. The processes are also suitable for short-run production.
An example of a selectivity method for the layer-by-layer processes here can be the application of susceptors, of absorbers, or of inhibitors, or the use of masks or the use of focused energy introduction, for example via a laser beam, or by way of glass fibers. Energy introduction is achieved by way of electromagnetic radiation.
Descriptions are given below of some processes with which moldings of the present invention can be produced from the powder of the present invention, but there is no intention that the present invention be restricted thereto.
One process which has particularly good suitability for the purposes of rapid prototyping is selective laser sintering. In this process, plastics powders in a chamber are selectively and briefly irradiated with light from a laser beam, the result being that the powder particles impacted by the laser beam are melted. The molten particles coalesce and rapidly solidify again to give a solid mass. Three-dimensional bodies can be simply and rapidly produced by this process via repeated irradiation of fresh layers repeatedly applied.
The patent specifications U.S. Pat. No. 6,136,948 and WO 96/06881 (both DTM Corporation) describe in detail the process of laser sintering (rapid prototyping) to produce moldings from pulverulent polymers. A wide variety of polymers and of copolymers is claimed for this use, examples being polyacetate, polypropylene, polyethylene, ionomers, and polyamide.
Other processes with good suitability are the SIB process as described in WO 01/38061, or a process as described in EP 1 015 214. Both processes operate with full-surface infrared heating to melt the powder. The selectivity of melting is achieved in the first process via application of an inhibitor, and in the second process via a mask. DE 103 11 438 describes another process. In this, the energy needed for the melting process is introduced via a microwave generator, and the selectivity is achieved via application of a susceptor.
Other suitable processes are those that operate with an absorber, either present within the powder or applied via ink jet methods, as described in DE 10 2004 012 682.8, DE 10 2004 012 683.6, and DE 10 2004 020 452.7.
The rapid prototyping processes or rapid manufacturing processes (RP processes or RM processes) can use pulverulent substrates, in particular polymers, preferably selected from polyester, polyvinyl chloride, polyacetal, polypropylene, polyethylene, polystyrene, polycarbonate, poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate (PMMA), ionomer, polyamide, or mixtures thereof.
U.S. Pat. No. 6,110,411 describes, specifically for laser sintering, powders of block copolymers which are comprise a hard segment and of a soft segment, where the hard block can comprise a polyamide unit, but the soft block comprises another component, namely of ether units and of ester units. The structure of the soft segments is described generally via the formulae (1) or (2):—O-G-O—C(O)—R—C(O)—  (1)—O-D-O—C(O)—R—C(O)—  (2)in which R is the radical of a dicarboxylic acid and G and, respectively, D is that radical of a glycol and, respectively, long-chain diol/polyetherdiol which remains after abstraction of the terminal hydroxy groups. The suitability, mentioned in the same publication, of polyether block amides of the PEBAX® series likewise refers to polyamide elastomers in which polyether segments and aliphatic polyamide segments have been linked to one another via ester groups.
The powders described above moreover have to comprise a powder-flow aid and have to have a glass transition temperature below 50° C. However, there is no feasible method based on polyamides for preparing stable block copolymers with a defined structure, with the exception of the polyetheresteramides (PEBA) included in the cited application and of the polyetheramines (PEA) not included in the cited application. Transamidation reactions usually occur in the melt comprising polyamides, until random distribution of the monomers has been reestablished.
DE 44 33 118 considers polymer blends. However, a blend is a mixture prepared from two or more polymers under defined conditions of temperature and shear, and usually processed to give pellets. In this process, the individual polymer chains are mixed with one another (“intermolecularly”), but no combination of the starting components occurs within one chain (for an example of a definition see Sächtling Kunststofftaschenbuch [Plastics Handbook], 24th edition, pp. 7 et seq.).
EP 0 060 579 A1 describes a polyetheramine in combination with a nylon 6 or 6,6. The solution viscosity of the copolymers considered is from 2 to 3.5. Due to increased water absorption, the material is unsuitable for the moldless production processes described above, and is impossible or very difficult to grind.
U.S. Pat. No. 5,296,062 treats powders with markedly different melting points. The main use is the adhesive-bonding of a relatively high-melting metal component to a component which comprises metal or of plastic and which has a lower melting point. The particles here may be present adjacent to one another, or the lower-melting-point component is applied as a coating to the other component. No homogeneous mixture within a powder particle is involved.
U.S. Pat. No. 6,143,852 describes a copolymer which comprises methyl methacrylate with C2-C10 alkyl methacrylate, and which is obtained via dispersion polymerization. This gives very small particles and a very narrow grain size distribution. However, the poor flowability of small particles makes them relatively unsuited to laser sintering; a narrow grain distribution such as that described leads to more difficult processing in a layer-by-layer process in which regions are melted selectively, specifically by virtue of narrow processing latitude, which in the extreme case can result in unsuitability.
WO 95/11006 describes a polymer powder suitable for the laser sintering process and exhibiting no overlap of the melting peak and recrystallization peak when melting behavior is determined via differential scanning calorimetry at a scanning rate of from 10 to 20° C./min, having a degree of crystallinity of from 10 to 90%, likewise determined via DSC, a number-average molecular weight Mn of from 30,000 to 500,000, and a Mw/Mn quotient in the range from 1 to 5.
DE 197 47 309 describes the use of a nylon 12 powder with increased melting point and increased enthalpy of fusion, obtained via re-precipitation of a polyamide previously prepared via ring-opening and subsequent polycondensation of laurolactam. This is a nylon 12.
A disadvantage of known components is poor impact resistance. This is similarly poor to that found in injection-molded polyamide components. Particularly if the intended use extends beyond the prototyping process, an example being small runs, good impact resistance of the components is essential, however. In the case of use in the automotive sector, components also have to retain adequate impact resistances even at low temperatures.
Another disadvantage is that impact-resistance modification methods found for granular materials cannot be transferred to pulverulent materials. Appropriately modified compound materials are generally not grindable, or only with yields which do not permit commercial use.